Interference is the main limitation faced by today wireless technologies, mainly due to the network densification, user density and the exponential increase in wireless data traffic verified in over the last few years. The dynamic nature of wireless communications further exacerbates the interference problem as the transmission and reception entities are unable to adapt as fast as the radio environment dynamics. Namely, when the transmission and reception entities adapt the network state may be already different and then the adaptation instead of being beneficial is detrimental.
Channel gain information is a crucial component for enhancing the throughput of current and future wireless systems, by enabling the adaptation of the transmission and reception entities to the network state. Channel gain information, when available, may be utilized to improve the system multiplexing gain, i.e. to simultaneously send data to multiple receivers.
The channel is usually estimated at the receivers and then fed back to the transmitter or transmitters. This procedure leads to a delay in the availability of channel gain information at the transmitter or transmitters. If the delay is larger than the channel coherence time, due to high mobility for example, the current channel realization cannot be predicted by the received channel gain information. Therefore, the use of predicted channel gain information based on outdated information leads to no multiplexing gain. However, when only one transmitter is considered, this transmitter is the only source of interference and then the delayed channel gain information may be used to reconstruct the previously generated interference (at one or more receivers) and format future transmit signals to be useful to more than one receiver (see M. A. Maddah-Ali and D. Tse, “Completely Stale Transmitter Channel State Information is Still Very Useful,” IEEE Trans. Inform. Theory, vol. 58, no. 7, pp. 4418-4431, July 2012). In contrast, when at least two transmitters simultaneously transmit there are two sources of interference and since that each transmitter only has access to its transmitted symbol stream, each transmitter is unable to reconstruct the whole past interference.
For the single transmitter case, the delayed channel gain information is used to determine combinations of the transmitted symbols that were received by the various receiving nodes in previous transmissions (under those channel gains). Based on this knowledge, the transmitter decides how to recombine the symbols intended for different users in the current transmission to aid the receivers to decode the data they needed (see U.S. Pat. No. 8,748,995 B2).
However, when more than one transmitter is present many state of the art approaches try to convert the case with more than one transmitter to the single transmitter case, by transmitting some redundancy together with the symbol stream. By doing this the receivers remove part of the interference and leave behind several linear combinations where only one transmitter is the interferer (see M. J. Abdoli, A. Ghasemi, and A. K. Khandani, “On the Degrees of Freedom of K-User SISO Interference and X Channels With Delayed CSIT,” IEEE Trans. Inform. Theory, vol. 59, no. 10, pp. 6542-6561, October 2013). Contrarily to the case where more than one transmitter causes interference, the corresponding interferer can reconstruct the remaining interference terms and retransmit them.
For all previously proposed methods, as the number of transmitter/receiver pairs increases the number of interference retransmissions required increases proportionally. As a consequence, the throughput achieved by all previously proposed methods does not scale with the number of transmitter/receiver pairs. To illustrate, when a large number of transmitter/receiver pairs are considered the throughput is at most equal to two symbols per time slot.
These facts are disclosed in order to illustrate the technical problem addressed by the present disclosure.